This invention relates to filament reinforced metal matrix structure and the method of and apparatus for making such structure. The invention contemplates the manufacture of such structure by placing alternate layers of metal and fiber reinforcements on top of each other around a hollow form, placing this assembly into a female mold, then consolidating the layers into a metal matrix by the application of internally applied pressure to the form while the assembly is maintained at a high temperature. Gases may be evacuated to minimize oxidation of the matrix material. The consolidation takes place by plastic flow densification, melting and/or diffusion bonding.
Other methods of making filament reinforced materials are known. Cochran et al in U.S. Pat. No. 3,547,180 teaches one method of producing reinforced composites. In the method of Cochran et al fibrous material, such as sapphire whiskers, is infiltrated with molten aluminum. This is done by placing a fibrous skeleton in an aluminum mold. The mold and its contents, together with an aluminum billet, are heated to at least 500 C., after which it is evacuated of gases. The temperature is then increased above the melting point of the aluminum billet. Pressure is next applied to force molten aluminum to infiltrate the fibrous skeleton within the mold. After cooling, the composite is removed from the mold and subjected to any further processing, such as machining.
Divecha et al in U.S. Pat. No. 3,668,748 discloses means for producing a fiber reinforced metal composite of desired shape. The metal matrix and fibers are integrated under pressure with the mixture maintained at a temperature wherein the matrix system is partly in the liquid and partly in the solid phase, enabling consolidation through extrusion in a die cavity.
Richardson et al in U.S. Pat. No. 3,377,657 discloses a method of molding reinforced plastic pipe. The pipe is nonmetallic being typically comprised of a corrosion resistant plastic lining encased within resin impregnated fibrous tapes having longitudinal reinforcing strands. A mandrel is used for laying up the tape.
Sara in U.S. Pat. No. 3,571,901 describes means for improving the wettability of carbon fibers which are to be imbedded in an aluminum composite article. Sara achieves improved wetting of the carbon fibers by first coating them with silver or silver-aluminum based alloys.
Pratt in U.S. Pat. No. 3,290,728 describes means for forming reinforced plastic pipe. Typically, the reinforcing material can be paper, asbestos, glass webs, glass filaments, or glass fabrics. One of the features of the invention is the utilization of a mandrel having an expansible sleeve or diaphragm on its exterior surface which can be internally pressurized to force the pipe material against an encircling mold during heat curing of the resin.
For purposes of this discussion, the term "filament" shall mean monofilaments, rovings comprising monofilaments, staple fibers, and thread or yarn made from staple fibers, short whiskers, etc. The physical form of such reinforcements is not critical to the practices of this invention.
There are materials, notably certain glasses, fused silica, and quartz which, when softened, retain sufficient strength to expand like an elastomeric material. Our invention makes use of these materials operating in the temperature range normally used for consolidating metal matrices to form metal matrix composites. In general, the consolidation temperatures are maintained so that the matrix system is partly in the liquid and partly in the solid phase.
It will be shown that over a specifiable temperature range, the walls of a softened glass container can be expanded under the influence of pressure to make metal matrix material positioned over the glass container to conform to the shape of a cavity. This is an improvement over prior art methods which, in general, utilize extrusion dies and expandable metal mandrels.